This project will test the hypothesis that K+o-dependent R222Q dysfunction results in increased arrhythmia frequency, particularly in Purkinje cells, and subsequently results in the development of DCM. Specific Aim 1: Test the hypothesis that human R222Q myocytes display potassium dependent arrhythmogenic properties. The sub-aims: (1) Test the hypothesis that human myocytes carrying the R222Q variant display EP differences when compared to control. Methods: (a) Myocytes generation from iPSC (b) EP characterization will be used to in order to determine basic sodium, potassium, and calcium channel gating properties of the R222Q variant versus control at normal and low K+. (2) Test the hypothesis that the R222Q variant in human myocytes results in potassium-dependent arrhythmias Method: iPS R222Q and control myocytes will be exposed to low potassium on day 35 following initiation of differentiation. Assessments include (a) Afterdepolarization frequency using patch clamping to measure single cell arrhythmia susceptibility (b) CardioExcyte to measure variability across cells in APD and in susceptibility to AD population wide arrhythmia susceptibility. Specific aim 2 Test the hypothesis that Purkinje cells are required for the arrhythmias and that arrhythmias result in DCM. The sub-aims: (1) Examine Purkinje cells as a possible mechanism for the arrhythmia-prone substrate. Method: Compare arrhythmia frequency in Langendorff- perfused mutant mouse hearts before and after Purkinje system ablation using Lugol's iodine solution at low (2 mM) extracellular potassium. (2) Determine if chronic exposure of low potassium leads to arrhythmias and/or DCM phenotype in vivo. Method: Compare arrhythmia frequency and echo indices of cardiac function in wild-type and mutant mice fed a potassium- free chow. Endpoints: Taken together these aims will test my hypothesis that low extracellular potassium, leads to arrhythmias (especially in the Purkinje network) and that frequent arrhythmias then cause R222Q-related DCM. Determining if arrhythmias precede DCM would help provide a treatment strategy for individual harboring this variant.